High load-carrying turbo oils containing amine phosphate and thiosemicarbazide derivatives

ABSTRACT

This invention relates to synthetic based turbo oils, preferably polyol ester-based turbo oils which exhibit exceptional load-carrying capacity by use of a synergistic combination of sulfur (S)-based and phosphorous (P)-based load additives. The S-containing additives of the present invention are thiosemicarbazide and its derivative, and the P-containing component is one or more amine phosphates. The turbo oil composition consisting of the dual P/S additives of the present invention achieves an excellent load-carrying capacity, which is better than that obtained when each additive was used alone at a treat rate higher than or comparable to the total combination additive treat rate, and the lower concentration requirement of the P-based additive allows the turbo oil composition to meet U.S. Navy MIL-L-23699 requirement on the Si seal compatibility.

This is a continuation of application Ser. No. 577,783, filed Dec. 22,1995, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to synthetic oil-based, preferably polyolester-based turbo oils which use a synergistic combination ofphosphorous (P)-based and sulfur (S)-based load additive chemistrieswhich allows the turbo oil formulation to impart exceptionally highload-carrying capacity and also to meet MIL-L-23699 Si sealcompatibility requirement.

2. Detailed Description

A turbo oil having unexpectedly superior load-carrying capacitycomprises a major portion of a synthetic base oil selected from diestersand polyol ester base oil, preferably polyol ester base oil, and minorportion of a load additive package comprising a mixture of aminephosphate and thiosemicarbazide or one of its derivatives and mixturesthereof.

The diester, which can be used in the high load-carrying lubecomposition of the present invention is formed by esterification oflinear or branched C₆ to C₁₅ aliphatic alcohols with one of such dibasicacids as sebacic, adipic, azelaic acids. Examples of diester aredi-2-ethyhexyl sebacate, di-octyl adipate.

The preferred synthetic base stock which is synthetic polyol ester baseoil is formed by the esterification of aliphatic polyols with carboxylicacids. The aliphatic polyols contain from 4 to 15 carbon atoms and havefrom 2 to 8 esterifiable hydroxyl groups. Examples of polyols aretrimethylolpropane, pentaerythiritol, dipentaerythritol, neopentylglycol, tripentaerythritol and mixtures thereof.

The carboxylic acid reactants used to produce the synthetic polyol esterbase oil are selected from aliphatic monocarboxylic acids or a mixtureof aliphatic monocarboxylic acids and aliphatic dicarboxylic acids. Thecarboxylic acids contains from 4 to 12 carbon atoms and includes thestraight and branched chain aliphatic acids, and mixtures ofmonocarboxylic acids may be used.

The preferred polyol ester base oil is one prepared from technicalpentaerythritol and a mixture of C₄ -C₁₂ carboxylic acids. Technicalpentaerythrtol is a mixture which includes about 85 to 92%monopentaerythritol and 8 to 15% dipentaerythritol. A typical commercialtechnical pentaerythritol contains about 88% monopentaerythritol havingthe structural formula: ##STR1## and about 12% of dipentaerythritolhaving the structural formula: ##STR2## The technical pentaerythritolmay also contain some tri and tetra pentaerythritol that is normallyformed as by-products during the manufacture of technicalpentaerythritol.

The preparation of esters from alcohols and carboxylic acids can beaccomplished using conventional methods and techniques known andfamiliar to those skilled in the art. In general, technicalpentaerythritol is heated with the desired carboxylic acid mixtureoptionally in the presence of a catalyst. Generally, a slight excess ofacid is employed to force the reaction to completion. Water is removedduring the reaction and any excess acid is then stripped from thereaction mixture. The esters of technical pentaerythritol may be usedwithout further purification or may be further purified usingconventional techniques such as distillation.

For the purposes of this specification and the following claims, theterm "technical pentaerythritol ester" is understood as meaning thepolyol ester base oil prepared from technical pentaerythritol and amixture of C₄ -C₁₂ carboxylic acids.

As previously stated, to the synthetic oil base stock is added a minorportion of an additive comprising a mixture of one or more aminephosphate(s) and thiosemicarbazide, its derivatives or mixtures thereof.

The amine phosphate used includes commercially available monobasic aminesalts of mixed mono- and di-acid phosphates and specialty amine salt ofthe diacid phosphate. The mono- and di-acid phosphate amines have thestructural formula: ##STR3## where R and R¹ are the same or differentand are C₁ to C₁₂ linear or branched chain alkyl

R₁ and R₂ are H or C₁ to C₁₂ linear or branched chain alkyl

R₃ is C₄ to C₁₂ linear or branched chain alkyl, or aryl-R₄ or R₄ -arylwhere R₄ is H or C₁ -C₁₂ alkyl, and aryl is C₆.

The preferred amine phosphates are those wherein R and R¹ are C₁ -C₆alkyl, and R₁ and R₂ are H or C₁ -C₄, and R₃ is aryl-R₄ where R₄ islinear chain C₄ -C₁₂ alkyl or R₃ is linear or branched chain C₈ -C₁₂alkyl.

The molar ratio of the mono- and diacid phosphate amine in thecommercial amine phosphates of the present invention ranges from 1:3 to3:1. Mixed mono-/di-acid phosphates and just diacid phosphate can beused, with the latter being the preferred.

The amine phosphates are used in an amount by weight in the range 50 to300 ppm (based on base stock), preferably 75 to 250 ppm, most preferably100 to 200 ppm amine phosphate.

Materials of this type are available commercially from a number ofsources including R. T. Vanderbilt (Vanlube series) and Ciba Geigy.

The sulfur containing additives used in this invention arethiosemicarbazides of the structural formula: ##STR4## wherein R⁵, R⁶,R⁷ and R⁸ are the same or different and are hydrogen, C₁ -C₈ alkyl, C₂-C₈ alkenyl, phenyl, mono- and di-C₁ -C₄ alkyl phenyl, allyl, ##STR5##where R⁹ is C₁ -C₈ alkyl. Preferably at least 2 of R⁵, R⁶, R⁷ and R⁸ arehydrogen, more preferably at least 3 of R⁵, R⁶, R⁷ and R⁸ are hydrogen,most preferably all four are hydrogen. Examples of thiosemicarbazideswhich can be used in the present invention are thiosemicarbazide per se(R⁵ -R⁸ are hydrogen), 1-allyl-3-thiosemicarbazide,1-acetyl-3-thiosemicarbazide (R⁹ is methyl),2,4-dimethyl-4-phenyl-3-thiosemicarbazide (R⁹ is methyl),2,4-dimethyl-4-phenyl-3-thiosemicarbazide,4,4-dimethyl-3-thiosemicarbazide, 4-methyl-3-thiosemicarbazide,4-ethyl-3-thiosemicarbazide.

The thiosemicarbazide(s) is (are) used in an amount by weight in therange 100 to 1000 ppm (based on polyol ester base stock), preferably 100to 500 ppm, most preferably 100 to 300 ppm.

The amine phosphate(s) and the thiosemicarbazide, its derivatives ormixtures thereof are used in the weight ratio of 1:1 to 1:10, preferably1:1 to 1:5, most preferably 1:2 to 1:3 aminephosphate(s):thiosemicarbazide(s).

The synthetic oil based, preferably polyol ester-based highload-carrying oil may also contain one or more of the following classesof additives: antioxidants, antifoamants, antiwear agents, corrosioninhibitors, hydrolytic stabilizers, metal deactivator, detergents. Totalamount of such other additives can be in the range 0.5 to 15 wt %,preferably 2 to 10 wt %, most preferably 3 to 8 wt %.

Antioxidants which can be used include aryl amines, e.g.,phenyl-naphthylamines and dialkyl diphenyl amines and mixtures thereof,hindered phenols, phenothiazines, and their derivatives.

The antioxidants are typically used in an amount in the range 1 to 5%.

Antiwear additives include hydrocarbyl phosphate esters, particularlytrihydrocarbyl phosphate esters in which the hydrocarbyl radical is anaryl or alkaryl radical or mixture thereof. Particular antiwearadditives include tricresyl phosphate, t-butyl phenyl phosphates,trixylenyl phosphate, and mixtures thereof.

The antiwear additives are typically used in an amount in the range 0.5to 4 wt %, preferably 1 to 3 wt %.

Corrosion inhibitors include, but are not limited to, various triazols,e.g., tolyl triazol, 1,2,4-benzene triazol, 1,2,3-benzene triazol,carboxy benzotriazole, alkylated benzotriazol and organic diacids, e.g.,sebacic acid.

The corrosion inhibitors can be used in an amount in the range 0.02 to0.5 wt %, preferably 0.05% to 0.25 wt %.

Lubricating oil additives are described generally in "Lubricants andRelated Products" by Dieter Klamann, Verlag Chemie, Deerfield, Fla.,1984, and also in "Lubricant Additives" by C. V. Smalheer and R. KennedySmith, 1967, pages 1-11, the disclosures of which are incorporatedherein by reference.

The turbo oils of the present invention exhibit excellent load-carryingcapacity as demonstrated by the severe FZG gear test, while meeting Siseal compatibility requirement set out by the United States Navy inMIL-L-23699 Specification. The polyol ester-based turbo oils to whichhave been added a synergistic mixture of the amine phosphate and theDMTD derivative produce a significant improvement in antiscuffingprotection of heavily loaded gears over that of the same formulationswithout the amine phosphate and the DMTD derivative, and furthermore,attain the higher load capability than that achieved with one of thesetwo additives used alone at a concentration greater than or comparableto that of the total S/P additive combination.

The present invention is further described by reference to the followingnon-limiting examples.

EXPERIMENTAL

In the following examples, a series of fully formulated aviation turbooils were used to illustrate the performance benefits of using a mixtureof the amine phosphate and thiosemicarbazide derivative in theload-carrying and Si seal tests. A polyol ester base stock prepared byreacting technical pentaerythritol with a mixture C₅ to C₁₀ acids wasemployed along with a standard additive package containing from 1.7-2.5%by weight aryl amine antioxidants, 0.5-2% tri-aryl phosphates, and 0.1%benzo or alkyl-benzotriazole. To this was added various load-carryingadditive package which consisted of the following: 1) Amine phosphatealone: Vanlube 692, a mixed mono-/di-acid phosphate amine, soldcommercially by R. T. Vanderbilt. 2) Thiosemicarbazide alone:thiosemicarbazide per se and 1 allyl-3-thiosemicarbazide. 3) Combination(present invention): the combination of the two materials described in(1) and (2).

The load-carrying capacity of these oils was evaluated in the severe FZGgear test. The FZG gear test is an industry standard test to measure theability of an oil to prevent scuffing of a set of moving gears as theload applied to the gears is increased. The "severe" FZG test mentionedhere is distinguished from the FZG test standardized in DIN 51 354 forgear oils in that the test oil is heated to a higher temperature (140°versus 90° C.), and the maximum pitch line velocity of the gear is alsohigher (16.6 versus 8.3 m/s). The FZG performance is reported in termsof failure load stage (FLS), which is defined as a lowest load stage atwhich the sum of widths of all damaged areas exceeds one tooth width ofthe gear. Table 1 lists Hertz load and total work transmitted by thetest gears at different load stages.

                  TABLE 1                                                         ______________________________________                                        Load Stage Hertz Load (N/mm.sup.2)                                                                     Total Work (kWh)                                     ______________________________________                                        1          146           0.19                                                 2          295           0.97                                                 3          474           2.96                                                 4          621           6.43                                                 5          773           11.8                                                 6          927           19.5                                                 7          1080          29.9                                                 8          1232          43.5                                                 9          1386          60.8                                                 10         1538          82.0                                                 ______________________________________                                    

The results from the severe FZG are shown in Table 2. The wt %concentrations (based on the polyol ester base stock) of the aminephosphate and DMTD derivative, either used alone or in combination, arealso specified in the tables. Table 2 demonstrates that the combinationof the amine phosphate and the DMTD derivative exhibits an excellentload-carrying capacity, which is better than that attributed to eachadditive used alone at a higher or comparable treat rate. The lowerP-based additive concentration requirement to achieve the highload-carrying capacity allows the synergistic P/S loadadditive-containing formulation to meet the MIL-L-23699 Si sealspecification.

                  TABLE 2                                                         ______________________________________                                        Load Additives          Severe FZG FLS                                        ______________________________________                                        None                    4                                                     0.02 wt % Vanlube (VL) 692                                                                            5.3 (6 runs)                                          0.02 wt % thiosemicarbazide                                                                           6                                                     0.03 wt % thiosemicarbazide                                                                           6                                                     0.05 wt % thiosemicarbazide                                                                           7                                                     0.02 wt % 1 allyl-3-thiosemicarbazide                                                                 6                                                     0.01 wt % VL 692 + 0.01 wt % thiosemicarbazide                                                        7.5 (2 runs)                                          0.01 wt % VL 692 + 0.02 wt % 1-allyl derivative                                                       6.4 (4 runs)                                          of thiosemicarbazide                                                          ______________________________________                                    

What is claimed is:
 1. A method for enhancing the load carrying capacityof a turbo oil comprising a base stock suitable for use as a turbo oilbase stock by adding to said turbo oil base stock a minor amount ofadditives comprising a mixture of thiosemicarbazide, its derivatives andmixtures thereof and one or more amine phosphate(s), wherein thethiosemicabazide is used in an amount in the range of 100 to 1000 ppmand is represented by the structural formula: ##STR6## wherein R⁵, R⁶,R⁷ and R⁸ are the same or different and are hydrogen, C₁ -C₈ alkyl, C₂-C₈ alklenyl, phenayl mono- and di- C₁ -C₄ alkyl phenyl, allyl, or##STR7## wherein R⁹ is C₁ -C₈ alkyl and wherein the amine phosphate isused in an amount in the range of 50 to 300 ppm and is of the formula:##STR8## wherein R and R' are the same or different and are C₁ -C₁₂linear or branched chain alkyl, R₁ and R₂ are H or C₁ -C₁₂ linear orbranched chain alky;R₃ is C₄ to C₁₂ linear or branched chain alkyl oraryl-R₄ or R₄ -aryl wherein R₄ is H or C₁ -C₁₂ alkyl and aryl is C₆. 2.The method of claim 1 wherein the base stock is a synthetic polyolester.
 3. The method of claim 2 wherein at least 2 of R⁵, R⁶, R⁷ and R⁸are hydrogen.
 4. The method of claim 2 wherein at least 3 of R⁵, R⁶, R⁷and R⁸ are hydrogen.
 5. The method of claim 1 wherein the aminephosphate and the thiosemicarbazide derivative are used in a weightratio of 1:1 to 1:10.
 6. The method of claim 1 wherein R and R' are C₁to C₆ alkyl, and R₁ and R₂ are H or C₁ -C₄, and R₃ is linear or branchedC₈ -C₁₂ alkyl.
 7. The method of claim 5 wherein the amine phosphate andthe thiosemicarbazide, its derivative(s) or mixture thereof are used ina weight ratio of 1:1 to 1:5.